A variety of carbamates have been developed since the 1960s for use as broad-spectrum insecticides. An easy and inexpensive in vitro assay using chick-embryo derived cells was examined for its capability to screen and test the toxicity of these compounds. Chick embryo brain and limb bud cultures were treated with different concentrations of either carbaryl or aldicarb with or without activation (k S-9) for 5 days. Viability and cytotoxicity using the neutral red assay, and carbamate effects on cell migration and colony spread were measured. S-9 decreased the effects of carbaryl and aldicarb on brain cell cytotoxicity at exposures of 15-60 ppm and 40-200 ppm, respectively, as indicated by increased concentrations of neutral red. Viability of brain cell cultures was not altered by aldicarb, but was decreased by carbaryl plus S-9 in concentrations of >40 ppm. In limb cultures, carbaryl without S-9 was significantly toxic at 8-25 ppm, but only concentrations of >25 ppm of carbaryl plus S-9 significantly affected cytotoxicity. In contrast, aldicarb without S-9 caused no effect on limb cell cytotoxicity at concentrations of 40-200 ppm, but aldicarb plus S-9 significantly reduced cellular cytotoxicity at concentrations of >160 ppm. Carbaryl C S-9 decreased the spread of both brain and limb colonies; aldicarb 4 S-9 caused a significant increase in the spread of the brain but not limb colonies. These results suggest that toxicities of carbaryl and aldicarb can be detected in vitro, but that these two carbamates have a selective toxicity, with carbaryl toxic to both brain and limb buds and aldicarb more toxic to brain than limb cells. S-9 was more likely to decrease the toxicity of carbaryl than the toxicity of aldicarb.